The present invention relates to a method of recording and reproducing information and an apparatus for recording and reproducing information on and from an optical disk, and in particular, to a method of recording and reproducing information and a apparatus for recording and reproducing information on and from an optical disk using a pit edge recording method suitable for improving a recording density.
A method of demodulation for demodulating recording data by detecting a leading edge and a trailing edge of a change in a quantity of a reflected light (i.e. a waveform of a reproduced signal) obtained from an optical disk has been adopted for a digital audio disk (DAD). The principle of the data demodulation is described e.g. in "Introduction to Video Disk and DAD" by Iwamura (Corona Publishing Co. Japan), pp. 212-215. The demodulation is achieved by detecting variation points in the waveform of the reproduction signal, namely, the leading edge and the trailing edge thereof and producing a detection window from the leading edge and the trailing edge so as to attain reproduced data. According to the demodulation method used for the DAD, a correct demodulation is conducted under the conditions that assuming a data interval to be T, the detection window width is T/2 and the pulse representing variation points are located in a region of .+-.T/4. Consequently, an error occurs if a zero cross point (corresponding to a variation point) and is moved due to a noise, a waveform distortion, a rotation jitter, an eccentric jitter, etc. to be beyond the detection window. Although the leading edge and the trailing edge can be used as data in an optical disk of la write-once type, since an object disk for the recording and reproducing operations is directly irradiated with laser light pulses to effect a thermal recording thereon in a case of the write-once type disk, the positions of the leading edge and the trailing edge of a recording region (a pit or a magnetic domain) are likely to be easily influenced by a sensitivity characteristic of a recording medium and a jitter consequently, the positions are apt to be indefinitely shifted. In the case of the DAD, since the pits are manufactured in a photoresist forming process when the disk is produced, such a problem has not arisen.
When applying the pit edge recording system to an optical disk of the write-once type or an erasable type, it is essential to correct the edge shift of the leading edge and the trailing edge in any cases during a recording operation.